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distinction is debatable. 5) Extreme pathways are the minimal set of EFMs and
represent a convex basis.
In Fig. 8.11 and Fig. 8.12 the elementary modes for the network in Fig. 8.10
are shown. In Fig. 8.12 the internal reversible reaction v 7 is broken down into its
forward and backward directions, giving rise to two reactions: v 7 and v 8 . As a
consequence the new stoichiometric matrix N is
1
0
0
0
1
1
0
0
0
1
0
1
1
0
1
1
N
=
0
0
0
0
0
1
1
1
0
0
1
1
0
0
0
0
and, with respect to Fig. 8.10, a new elementary mode is added, namely the one
depicted in the last box.
For each reversible internal reaction, the set of EFMs and EPs in the modified
network includes at least a 'cycle'. However, these particular fluxes are not
considered, since EFMs and EPs are important to understand the exchange of
fluxes between external and internal metabolites. In Table 8.3, the relations
between EFMs and EPs in Fig. 8.10 are shown.
Nonnegative combinations of EPs in the third column are shown to determine
EFM'1 and EFM'5.
Fig. 8.10. Elementary flux modes for the network in Fig. 8.9. The corresponding flux vector in the
null of the matrix N are shown at the bottom of each box.
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